It is thought that 50 GW of power might be extracted from a dam built across the Red Sea, and which might alleviate tensions in the Middle East related to energy. Opponents to the idea think that the scheme could create environmental damage on a huge scale and even displace millions of people from their homes. The environmental costs must presumably be weighed against those from CO2 emissions which it is argued the project would save and easing demand on other resources which will run short within a few decades. The dam would need to be 18 miles across, to match the sweep of the Red Sea where it opens into the Gulf of Aden, it's narrowest point.
Hydropower is clean and entirely renewable, albeit there are arguments to the effect that the creation of dams, when areas of land are deliberately flooded, cause the release of methane, another gas thought responsible for global warming. Presumably there would also be some flooding of coastal regions in this project, which would be a stupendous feat of civil engineering. Regarding a timescale, one estimate of 25 years has been given, in comparison with that incurred in building other large dams.
The largest existing hydropower installation is powered by the Italpu Dam at the Paraguayan Brazilian border, which produces 12.6 GW of electricity, and the Three Gorges Dam in China is due for completion in 2009, and more than one million people were displaced during its construction: hence the fears among environmentalists that a similar outcome may befall coastal populations around the Red Sea. The Three Gorges dam generates 13.4 GW and when it is fully operational is expected to increase its output to 22.5 GW. By way of contrast, the Niagara Falls generates just 2.5 GW, taking 90% of the flow of water that flows over the falls themselves.
As ever there are many issues to be considered, but the world may need all the hydropower it can get, rather than using nonrenewable fuels to produce electricity such as gas, coal and uranium, supplies of which may be under quite some pressure in 25 years time, if not before then. However, it is clear that we can't have it both ways, i.e. preserve our energy-rich lifestyle and avoid environmental impacts whether they be on land, sea or the atmosphere, in their interconnected entirety.
"Proposal: 50 Gigawatts if they dam the Red Sea." By Rick C. Hodgin, http://www.tgdaily.com/content/view/35178/113/